values of births that did not take place, such present values being determined as the difference between the discounted value of the expected life-time consumption and income streams. The application of a discount rate that is realistic for ordinary investment decisions, that is a rate of the order of magnitude of 10 percent per year or higher, virtually takes away any significance from all effects that will be felt beyond 15 or 20 years. However, it could be argued that population problems are long-run problems par excellence and that it is the special responsibility of economists to clarify the important long-term implications of alternative levels of current fertility, whether or not the incidence of the effects falls within the present time horizon of policymakers. Such clarification is needed quite independently from any economic arguments that would seek to establish the proper rates of time discount that should be applied in formulating public policies.
Second, even if one were prepared to give primacy to short-run considerations, it would seem that the essential economic difference between maintaining fertility at its original high level and drastically reducing it cannot be expressed at all adequately by a catalog of items not consumed because of fewer births and by a quantitative valuation of the items so "saved" and their immediate economic repercussions. Twenty years from now a society that has undergone a revolutionary transformation of the age-old patterns of reproductive behavior will be a society qualitatively different from one in which no such transformation took place. It is difficult to envisage a situation without these qualitative differences also manifesting themselves in multifarious ways in practically all economically significant aspects of human behavior. Massive adoption of new ideas on family size accompanied by action translating these new ideas into reality is inconceivable without a massive breakthrough in spreading and strengthening patterns of rational economic behavior; in inculcating and reinforcing the idea that individual action can improve one's economic status; in effecting favorable changes in economic mobility, initiative, risk-taking, and economic calculus; in promoting modern attitudes on child rearing and education; in raising aspirations and goals of achievement for the individual, his family, and his children; and in changing many other aspects. Much more attention should be given to attempts to verify empirically such intangible relations and, as far as possible, to measure their practical significance.
Third, the same factors that are responsible for an undue emphasis on short-term effects explain why little systematic attention has been given to population size and density as such. To a certain extent the professional literature on this score is in felicitous contrast to much of the popular debate that centers around "overpopulation." A discussion of "resources" and "food" is largely missing in the literature partly because the optimistic notion that sudden changes of fertility could greatly change the parameters of these problems 5 or even 10 years hence is considered a fallacy; and partly because